Nearshore Ecosystems Overview

THE NEARSHORE ECOSYSTEM IS WHERE LAND AND OCEAN MEET. FRESH AND SALT WATER AND LAND-BASED AND OCEANIC NUTRIENTS ARE CONTINUOUSLY BEING EXCHANGED. A DYNAMIC AND SPECIALIZED ARRAY OF SPECIES IS ADAPTED TO SURVIVE THE VARIATION OF IMMERSION IN SALT WATER AND EXPOSURE TO AIR. IN THIS CONCEPTUAL NEARSHORE FOODWEB MODEL, SEA OTTERS, BLACK OYSTERCATCHERS, SEA DUCKS, AND SEA STARS ACT AS THE TOP-LEVEL CONSUMERS IN A SYSTEM WHERE PRIMARY PRODUCTIVITY ORIGINATES MOSTLY FROM THE SEAWEEDS AND SEA GRASSES AND MOVES THROUGH BENTHIC (BOTTOM-DWELLING) INVERTEBRATES.

Daily tide like breathexhale, reveal salt secretsLimpet on a rock

The nearshore ecosystem includes intertidal and subtidal zones that run along the coast. The intertidal zone ranges between the high and low tide lines. During low tides, intertidal areas are exposed to air and in some cases fresh water due to precipitation or runoff. During high tides, the same areas are inundated with salt water, submerging previously exposed habitat. In contrast, the subtidal zone is rarely or never exposed, but is highly influenced by its proximity to both the coastal areas and the ocean.

The nearshore ecosystem provides nursery grounds for marine invertebrates and fishes; nesting habitats for seabirds; pupping habitats for seals and sea lions; important feeding habitats for pelagic predators; primary resident habitat for sea otters, harbor seals, shorebirds, sea ducks, nearshore fishes such as sand lance, and marine invertebrates such as clams and mussels; and recreational, commercial, and subsistence opportunities for humans. The canopy forming kelps and eelgrass beds found in the nearshore provide primary production and structure to nursery habitats, and also can dissipate wave energy, thus reducing coastal erosion, and serve as a carbon “sink” capable of storing substantial amounts of atmospheric carbon dioxide.

The nearshore is also an important triple interface between air, land, and sea that provides linkages for transfer of water, nutrients, and species between watersheds and offshore habitats.

Why are we monitoring?

The nearshore ecosystem is broadly recognized as highly susceptible and sensitive to a variety of both natural and human disturbances on a variety of temporal and spatial scales. For example, observed changes in nearshore systems have been attributed to such diverse causes as global climate change, earthquakes, oil spills, human disturbance and harvest, and influences of invasive species. Both intertidal and subtidal communities and many species associated with the nearshore ecosystem, including clams, mussels, sea otters, and harlequin ducks, were among the most injured by the Exxon Valdez oil spill.

With more than 50 years of nearshore data collection in the spill-affected area, sustained monitoring of long-term trends in this ecosystem provides valuable information to state and federal agencies for resource management, for understanding sensitivity of this ecosystem to damage from possible future oil spills or other perturbations, and for evaluating the potential effects of climate change.

How are we monitoring?

The nearshore monitoring program focuses on the nearshore benthic food web in the northern Gulf of Alaska. Currently, the program evaluates six ecological indicators and more than 200 species that range from primary producers to top level consumers, and is designed to examine both bottom-up and top-down dynamics. By employing a spatial design that allows broad geographic inference and selecting species with direct food web linkages, our monitoring program simultaneously detects change and assesses potential mechanisms underlying that change.

What are we finding?

In recent years, the nearshore monitoring program has documented the following:

Mussel abundance declined Gulf of Alaska-wide, and subsequently recovered in some regions to varied extents and magnitudes. This variation in a primary prey resource has likely affected the food supply for top level predators in the nearshore ecosystem such as sea otters, sea ducks, and shorebirds.

Common murre populations made a dramatic shift in their distribution during the summer of 2015. We observed common murres in the nearshore ecosystem where no nesting colonies occur and where the species had been rarely or never observed in past years. These observations correspond to observations made by projects in the pelagic component and other studies of a large die-off of murres throughout the Gulf of Alaska and the north Pacific in winter 2015-2016.

Sea star wasting disease occurred and increased in prevalence from 2014 to 2015. In 2014, based on coast-wide concerns about sea star wasting disease, we began monitoring for the disease. The disease increased prevalence from 2014 to 2015 (0.6% to 3.4%), but the prevalence remained low in comparison to observations in southeast Alaska and the lower 48. Occurrences, however, may be underestimated due to the limited area of Alaska’s coastline that have been sampled.

Trends in sea otter populations diverged at three locations in the Gulf of Alaska. Our analysis of recent sea otter abundance in Kenai Fjords National Park, Katmai National Park, and Western Prince of Wales indicates populations with divergent trajectories, including growth, stability, and, perhaps most recently, decline. This spatial contrast among locations is one of the key design features of our monitoring program and suggests that mechanisms influencing sea otter abundance and trend can differ at relatively small scales. Further, these data suggest that sea otters in the Gulf of Alaska currently are not being driven by large scale (Gulf-of-Alaska-wide) factors operating more broadly. The divergent trends in sea otter abundance allow us to evaluate those trends independently, using the diet and mortality data collected concurrently at each block.

SCIENTISTS RECORD SPECIES OCCURRENCE OF SEAWEEDS AND INVERTEBRATE ANIMALS ALONG PERMANENT TRANSECT LINES WITHIN THE INTERTIDAL ZONE OF BEACHES EACH YEAR TO MONITOR CHANGES OVER TIME. HOW MANY KELPS DO YOU SEE? (PHOTO CREDIT: JAMES PFEIFFENBERGER, NPS OASLC)